Besides calling the PictureBox.LoadAsync method, the PictureBox.WaitOnLoad property must be set to false to load an image asynchronously. When you load an image asynchronously, you can handle the PictureBox.LoadProgressChanged event to determine the progress of an image load or the PictureBox.LoadCompleted event to determine when an image load has completed.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Assembly Versions: 2.0.0.0